This application claims the benefit of German Application Serial No.299 17 940.0, filed Oct. 12, 1999.
The invention pertains to a device for gravimetric testing of multi-channel pipettes which have two or more pipette channels.
Multi-channel pipettes are frequently used in laboratories, particularly in biosciences and medicine. One important advantage of multi-channel pipettes, which as a rule consist of 4, 8 or 12 channels, is that fewer pipetting processes are required. This makes possible significantly faster and more efficient working.
One embodiment form of multi-channel pipettes uses piston-stroke pipettes with air cushions, which allows the transfer of quantities of liquid in the xcexcL range. The replaceable plastic tip and the air cushion make possible to prevent contamination of the pipette, e.g., by radioactive or infectious material, in this kind of piston stroke pipette.
Manufacturers of multi-channel pipettes must establish proof of their measurement accuracy with conformance certification. In addition, certified laboratories regularly must check the measurement accuracy of their test apparatuses according to DIN EN ISO 9000; this also pertains to their multi-channel pipettes.
When testing the measurement accuracy of multi-channel pipettes, as a rule, the procedure according to DIN 12650 is used. In gravimetric testing according to DIN 12650-6, for example, first all channels of a piston stroke pipette are equipped with tips. For pre-moistening of the air cushion in tips and pipettes, five pipetting steps with water must be carried out before beginning the test. During pipetting, care must be taken that all channels are filled in order to prevent errors due to tipping effects resulting from irregular loading of the individual channels. Next, the contents of each channel will be pipetted into a tarred weighing vessel and the pipetted water volume determined by weighing.
For each channel, ten measurements are prescribed according to DIN 12650-6. Since multi-channel piston-stroke pipettes always allow a volume adjustment, the testing must be carried out at the rated volume, half the rated volume, and also at the smallest adjustable volume. Whereas in the case of the single-channel pipettes with a fixed volume, only ten measurements are needed, for a 12-channel piston stroke pipette, a total of 360 measurements will be required. Therefore, whereas the single-channel pipette will only require a test time of about 15 to 20 min, the 12-channel piston stroke pipette will require about 10 to 12 hs.
This large time requirement for conventional test methods for multi-channel pipettes shows the significant disadvantage of these test methods. Also, the evaluation of conventional test methods takes long time.
Proceeding from these disadvantages of the state of the art, the invention is based on the problem of specifying a device which allows the essentially automatic testing of a multi-channel pipette and which reduces the time necessary for the testing. In addition, the device should allow an automatic evaluation of the test results.
This problem is solved by the main patent claim. The subordinate claims pertain to favorable embodiments and refinements of the invention.
A device is proposed for gravimetric testing of multi-channel pipettes which have two or more pipette channels, with one receptacle per pipette for a test volume or for a container containing the test volume, and one weighing cell per receptacle for weighing the container and/or the test volume. In addition, for each receptacle the device features one weighing cell for weighing the container or the test volume, or for simultaneous weighing of container and test volume.
With a device of this kind, it is possible to reduce significance the time required for the testing of multi-channel pipettes because a parallel measurement and evaluation of the individual pipette channels can occur. Thus, according to the present invention, both the pipetting and the weighing for all pipette channels of a multi-channel pipette can be conducted simultaneously. In addition, when using the device according to the present invention, it is possible to implement a fully automatic evaluation of the weighing results. For complete testing of a 12-channel pipette and evaluation of the measured results, the test time can thus be reduced significantly.
The test volume dosed through one pipette channel can be pipetted either directly into a correspondingly formed receptacle, or into a separate container which is held in the receptacle for measurement. Each receptacle, in turn, can rest directly upon the weighing cell assigned to the receptacle, or it can be connected via a linkage or a lever arrangement to the weighing cell. The particular configuration of the connection between receptacle and weighing cell depends in particular on the kind of weighing cell used. Due to a suitable selection of the type of weighing cell and of the connection between receptacle and weighing cell, the device according to the present invention can be used for the testing of a number of different commercially available multi-channel pipettes.